1. Field of the Invention
The present invention relates to a radio frequency processing apparatus of a wideband wireless local loop (W-WLL), and more particularly, to a radio frequency transmission control apparatus for preventing oscillation in a W-WLL terminal, in which power supply is controlled in accordance with characteristics of each active element of radio frequency transmitter unit in the W-WLL terminal, to thereby eliminate an oscillation caused by a simultaneous power supply to the radio frequency processing apparatus and minimize power consumption.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a radio frequency processing apparatus of a common W-WLL terminal.
Referring to FIG. 1, the radio frequency processing apparatus includes a radio frequency receiving unit 20 for demodulating an WLL radio frequency band signal received via an antenna to a baseband signal so as to be processed in a modem; a radio frequency transmitting unit 40 for modulating the baseband signal to a WLL radio frequency band signal and transmitting the modulated signal via an antenna; a local clock generating unit 30 for generating a local clock to be used in the radio frequency receiving unit 20 and radio frequency transmitting unit 40; and a BBM (baseband module) interface unit 50 for matching among a BBM for performing a signal processing in a W-WLL terminal, the radio frequency receiving unit 20 and radio frequency transmitting unit 40.
Referring to FIG. 2, the radio frequency receiving unit 20 further includes a power switch unit (VCC switch unit) 60 for controlling a power supply to operate the radio frequency receiving unit 20 in accordance with a control of the BBM interface unit 50; an LNA (low noise amplifier) 20a for reducing a noise in a signal output from an antenna duplex 10 and amplifying the noise-reduced signal; an RF BPF (radio frequency band pass filter) 20b for performing a band pass filtering to a radio frequency signal output from the LNA 20a; an LNA 20c for performing a low-noise amplification to the signal that has passed the RF BPF 20b; an RF BPF 20d for performing a band pass filtering to the signal that has passed the LNA 20c; a down-mixer 20e for mixing up the local clock generated from the local clock generating unit 30 and the signal that has passed the RF BPF 20d and generating an IF (intermediate frequency); an IF BPF (intermediate frequency radio frequency band pass filter) 20f for performing a band pass filtering to the signal that has passed the down-mixer 20e; an automatic gain control amplifier AGC IF 20g for converting an automatic control voltage in accordance with a level of the signal output from the IF BPF 20f so as to maintain an output signal at a regular level; an adder 20j for generating an automatic control voltage so as to maintain a signal output from the modem of W-WLL terminal at a regular level and providing the AGC IF 20g with thus-generated automatic control voltage; an IF amplifier 20k for amplifying a signal output from the AGC IF 20g; a demodulator 201 for demodulating a signal output from the IF amplifier 20k using the local frequency output from the local clock generating unit 30; and a data buffer 20m for buffering a signal output from the demodulator 201 and outputting the result to the BBM interface unit 50.
Thus-configured radio frequency receiving unit of a common W-WLL terminal operates as follows.
The BBM (digital signal processing apparatus of W-WLL RIU (radio interface unit) outputs a control signal RX_ON for power supply of the radio frequency receiving unit 20 and a gain control PDM signal of the local clock generating unit 30. Thus, the VCC switch unit 60 supplies power to each component constituting the radio frequency receiving unit 20, and the local clock generating unit 30 generates a local RF and local IF.
A forward channel RF signal transmitted from a W-WLL radio port is received via an antenna and input to the antenna duplex 10. Then, the antenna duplex 10 eliminates signals existing in an area excluding an applied bandwidth, and transmits the result to the LNA 20a. 
The LAN 20a amplifies the signal according to a supporting standard, and transmits the result to the RF BPF 20b. The RF BPF 20b has a bandwidth of 30 MHz, filters only a signal of bandwidth of 30 MHz, and transmits the result to the LNA 20c. The LNA 20c reduces noise of the input signal, amplifies the same, and transmits the same to the RF BPF 20d. The RF BPF 20d performs a filtering to enhance a noise figure, and outputs the result to the down-mixer 20e. 
The down-mixer 20e receives local RF (radio frequency higher than the received RF by the amount of IF) output from the RF VCO (voltage-controller oscillator) 30c of the local clock generating unit 30, and mixes the local RF with the signal output from the RF BPF 20d, to thereby generate an intermediate frequency (IF). This IF is for a conversion to a baseband.
The IF BPF 20f passes, among IFs output from the down-mixer 20e, only the bandwidth corresponding to the band of the processed signal of a modem of W-WLL terminal, and suppresses signals existing outside of the band and in the adjacent channel.
The AGC IF 20g has a unique gain control scope according to characteristics of component, and changes gain control voltage according to the input signal level, thus maintaining output signal at a regular level. The gain control signal is output from a modem.
The signal output from the AGC IF 20g is amplified in the IF amplifier 20k, and transmitted to the demodulator 20l. The demodulator 20l receives local IF output from the IF VCO 30e of the local clock generating unit 30. Using such a local IF, output signal of the IF amplifier 20k is demodulated by a QPSK (quadrature phase shift keying) method. I-signal and Q-signal which are demodulated to a baseband are buffered in the data buffer 20m and output to the BBM interface unit 50.
FIG. 3 illustrates configuration of a common radio frequency transmitting unit which operates as follows.
The radio frequency transmitting unit 40 modulates I-signal and Q-signal of the baseband transmitted from the BBM interface unit 50 to a QPSK signal, and converts the same to an RF signal using local RF signal and local IF signal. Then, the RF signal is amplified using a power amplifier 40k, and emitted via an antenna.
A power switch unit 70 of the radio frequency transmitting unit 40 supplies/cuts off power to/from each component of the radio frequency transmitting unit 40 in accordance with a power control signal output from the BBM interface unit 50. That is, when TXON signal in a high-active state is output from the BBM interface unit 50, the power switch unit 70 supplies power all over the active element of the radio frequency transmitting unit 40 through a single power supply line (TX_VCC) connected to the radio frequency transmitting unit 40.
When each active element of the radio frequency transmitting unit 40 is thus-provided with a power through the line (TX_VCC), an overload problem may occur. Further, an additional problem may occur in that the radio frequency transmitting unit 40 outputs an undesired oscillation frequency while I-signal (TX_I) and Q-signal (TX_Q) output from the BBM interface unit 50 are transmitted to the power amplifier 40k, i.e., the final amplifier, via the data buffer 40a. That is, the radio frequency transmitting unit 40 has an oscillation when a power switching is performed, thus deteriorating Eb/No value of RF module transmitting output. In addition, such an oscillation may reduce capacity of the radio port when a wireless communication is performed.
During the delay time period until the transmitting signals are sequentially input from the data buffer 40a, that is, during the time period where the operation of the power amplifier 40k is not required, the power amplifier 40k which ranks highest power consumption among active components of the radio frequency transmitting unit 40 operates, which may result in a power loss.
Further, the radio frequency transmitting unit 40 is turned off after the power amplifier 40k has finished outputting of the transmitting RF. Thus, other active elements except the power amplifier 40k may consume unnecessary power.
Therefore, it is an object of the present invention to provide a radio frequency transmission control apparatus for preventing an oscillation in a wideband wireless local loop terminal in which power supply is controlled in accordance with characteristics of each active element of radio frequency transmitter unit in the W-WLL terminal so as to thereby eliminate an oscillation caused by a simultaneous power supply to the radio frequency processing apparatus and minimize power consumption.
To accomplish the above object of the present invention, there is provided a radio frequency transmission control apparatus for preventing an oscillation in a wideband wireless local loop terminal, the apparatus has a radio frequency transmitting unit for modulating a baseband transmitting signal to a WLL radio frequency band signal and transmitting the modulated signal via an antenna, and which is divided into a radio frequency converting unit and a power amplifier unit in accordance with characteristics of each active element constituting the radio frequency transmitting unit. When a power is supplied to the radio frequency transmitting unit, the power is first supplied to the radio frequency converting unit so as to maintain the same at an operating state. After a predetermined time period has elapsed, the power is supplied to the power amplifier unit. When the radio frequency transmitting unit is cut off from a power, a cutoff of the power amplifier unit is performed prior to a cutoff of the radio frequency converting unit, to thereby prevent generation of an oscillation frequency in W-WLL terminal.